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Breakthroughs in Plasmonics

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When light hits a metal, it generates electromagnetic waves that travel along the surface of the metal. These waves, called surface plasmon polaritons (SPPs), can be harnessed to make powerful sensors and ultra-compact devices that relay data almost instantaneously.

One major obstacle in developing plasmonic devices, however, is dissipative loss. SPPs decay as they travel along the metal due to the conversion of optical energy to heat. These losses severely limit the performance of metal-based plasmonic devices at optical frequencies.

To overcome this problem, some scientists have proposed using waveguides – structures that confine and convey waves – that are made of only dielectric materials. These could enable modal-dispersion- induced effective SPPs that do not suffer dissipative losses.

Now, scientists at Nanyang Technological University’s School of Electrical and Electronic Engineering (EEE) have achieved the first experimental realisation of modal-dispersion-induced effective surface plasmon polariton (ESPP) propagation in an all-dielectric waveguide.

The EEE team is led by Professor Luo Yu. A schematic of their design is shown in the figures. Their work could improve the performance of plasmon-based optical devices, and help realise many other plasmonic capabilities, such as sub-wavelength focusing, super- resolution imaging and plasmonic cloaking.

Before the EEE team’s work, the existence of modal-dispersion-induced ESPPs had not been verified through experiments.

The team provided further theoretical insights into, and experimental verification of, the ESPPs by engineering transverse-electric modes in conventional rectangular waveguides.

They also derived the ESPPs’ complete field distributions, dispersion relations and asymptotic frequencies analytically, and designed wave-port excitations and smooth bridges for the mode conversion between propagating modes in rectangular waveguides and the ESPPs.

Their all-dielectric waveguide makes use of the structured transverse-electric mode in a conventional rectangular waveguide, and has the advantages of simple design and large propagation length.

Professor Luo added that their work opens up avenues for low-frequency designer surface plasmons, and could lead to compact filters, resonators and sensors of ESPPs in the microwave and terahertz frequencies.

Breakthroughsinplasmonics-730.jpg
 

By Professor Luo Yu

Click here to find out more.

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Published on: 30 November-2017 ​​​​​

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